[The Characteristics and Treatment Outcomes for Desmoid Tumors Associated with Familial Adenomatous Polyposis]

The characteristics of desmoid tumors(DTs)associated with familial adenomatous polyposis(FAP)and relationships between the development of DTs and the sites of APC germline mutation have not closely been examined Japan.This retrospective study was performed to address these issues by examining patients with FAP who underwent proctocolectomy between 1981 and 2015.The cumulative 2-year incidence of DT development was 50%. The DTs developed in the abdominal wall only in 2, in the abdominal wall plus intra-abdominally in 4, and intra-abdominally in 2. Clinical stages according to the Church's classification included Stage I in 3, Stage II in 2, Stage III in 1, and Stage IV in 2. Among 31 patients with a confirmed pathogenic germline APC mutation, patients with mutation in 3' site of codon 1400 (n=7)tended to develop DTs more frequently than those with mutation in 5' site of codon 1400(n=24)(p=0.08). The cumulative 5-year survival rate in patients with DT development was 73.3%. Including 2 patients undergoing initial colectomy at other institutions, the therapeutic efficacy in 4 patients with severe intraabdominal DTs(Stage III /Stage IV )who were given chemotherapy comprising doxorubicin plus dacarbazine(DOX plus DTIC)revealed partial response in 3 and complete response in 1. Febrile neutropenia was recorded in 2 of these patients.The frequency of DTs development and genotype-phenotype relationship of FAP patients seems to concur with those reported from Western countries. Since the DOX plus DTIC therapy for severe DTs is valid but toxicity is high, the development of less toxic regimens are warranted.